The invention concerns an arrangement for coupling microwave energy into a treatment chamber disposed in a cavity resonator, in particular a plasma CVD coating chamber, comprising a microwave feed and a microwave waveguide.
Apparatuses are known for producing a plasma which serves for example for coating, cleaning, modifying and etching substrates, but also for treating medical implants. Workpieces of the most widely varying shapes are coated. Known apparatuses for producing plasma have an annular resonator to which microwaves are fed by way of a waveguide and a coaxial cable.
The coating of motor vehicle tanks is also known, in which case four or more microwave sources in the form of magnetrons are arranged in the outside wall of the cavity resonator, in order to activate a gas which has been previously introduced into the tank, to the plasma state, by means of the coupled-in microwave energy. At least four magnetrons are required for a tank and, if a plurality of containers are to be simultaneously provided with an internal coating, the number of magnetrons with their power supply units increases to an economically non-viably high number. In addition it has been found that, depending on the respective size and configuration of the container to be coated, the losses and reflections of the coupled-in microwave energy differ to such an extent that, for a given configuration, it is necessary to implement an adaptation procedure which then no longer affords satisfactory results for the next, different configuration. Different loads, losses and reflection phenomena occur so that a more or less tedious adaptation and tuning procedure has to be implemented for each kind of container. Investigations have also already been conducted into the reflection factor of the microwave power in dependence on the length of the feed conduit to a microwave reaction chamber in order to achieve optimum tuning for given frequencies. A change in the pattern of the reflection effect in dependence on the length of a feed conduit has been achieved by introducing different absorbers into microwave waveguides, but in that case a sensitivity in regard to mismatching as a consequence of changes in geometry is always to be observed.